Secret signaling



July 2, 1935 l J. B. MOORE 2,006,961

SECRET SIGNALING Filed Nov. 11, 1952 T610/VSM! TT/NG INVENTOR- JOHN E1. MOORE ATTORNEY- Patcnte'd July 2, 1935 SECRET SIGNALING John B. Moore, Riverhead, N. Y., assigner to Radio Corporation of America, a corporation ot Delaware Application November 11, im, serai No. 642,195 s claim. (ci. ria-1.5)`

'lhis invention relates to communication systems of the type wherein messages or portions thereof are repeated a predetermined number of times. Such systems utilizing the repitition of signal characters are frequently used in the interest of accuracy in order to overcome fading or atmospheric disturbances, and for secrecy purposes. An illustrative arrangement of this type is described in United States Patent No. 1,677,062 granted July 10, 1928 to C. Verdan and L. Loiseau.

'I'hese systems, as known in the art, however, are designed primarily for telegraphic code cornmunication and vdo not lend themselves readily d for use with telephone circuits. It is, therefore,

a primary object of the present invention to enable the multiple transmission of voice currents in a simple and highly efficient manner. The achievement of this object in accordance with o the present invention renders the system to be hereinafter described adaptable for use on radio telephone channels where some means of obtaining privacy or secrecy of the conversations is essential.- 4

2'5 A further object is to provide a system wherein all kinds of messages, regardless of character, may be transmitted with a high degree of secrecy any desired number of times.

In general, the invention contemplates a system wherein the messages or signals to be transmitted are sub-divided at the transmitting terminal into a number of signal sections or units, a portion of each section or unit being repeated in one or more of the following units. These signal units are then transmitted in inverted order. At the receiving terminal the overlapping inverted units are restored to their original form by suitable apparatus which is arranged to function in synchronism with the apparatus at the transmitting end.

A better understanding of the invention may be had by referring to the following detailed description which is accompanied by a single drawing illustrating, diagrammatically, a complete communication system embodying the `preferred form of the present invention.

Although the invention to be hereinafter described is set forth with special regard tothe requirements of telephone circuits, either radio in conventional form; one method of practicingv 55 the present invention, in which the upperl poror landline, it is to be distinctly understood that tion of thesystem above the horizontal dotted lines comprises the transmitting equipment, the lower portion below the horizontal dotted lines comprises the receiving system, and the portion intermediate the dotted lines comprises any suitable medium over which signals may be sent, such as a landline, submarine cable, or radio channel.

The transmitting equipment consists, essentially, of an endless wire I, I of magnetic material which is stretched between two rotating drums or pulleys 3 and 4 which, in turn, are driven By a motor or other suitable apparatus. This wire, which may be made of iron or steel, is arranged to be moved past a group of electromagnetic coils and serves as a recording medium on which impressions corresponding to the signal being transmitted are made.

Speech currents present in the circuit as a result of talking into transmitter 5 are ampli- 20 fied by amplifier 6 and magnetize recording coil 1 which, in turn, applies the message to the endless wire I, I. Of course, any suitable means, such as asource of audio frequency tone I9 which can be keyed as indicated in the drawing, may be utilized instead of the speech transmitter to impress signels on the recording coil 1. A wiping coil 8 is suitably energized by battery I1 for removing the signals from endless wire I, I. This coil is positioned adjacent the drum or pulley 4 and opposite the recording apparatus 1 with respect to pick-up collector wheel 9.

Wheel 9 is composed of a plurality of pickup coils I0, II, I2, I3, etc. which are mounted at predetermined locations'around the periphery thereof. This wheel is arranged to be rotated in the same direction as wire I, I, but at a speed greater than twice the speed of endless wire I, I whereby the coils pass close to the 40 endless wire and pick up the signal impulses impressed thereupon and transfer these impulses to a stationary circuit which feeds suitable channel input equipment for transmission of the signals to the distant receiving station. Any suitable means, such as a synchronous motor may be used to rotate wheel 9, or, if desired, the pickup wheel shaft and the driving drums and the main driving shaft of the synchronous driving motor may be inter-connected by suitable gearing to maintain the relative velocities herein referred to. The angular spacing of the pick-up coils, the radial distance from the center of the wheel to the outer ends of the pole pieces of the coils, and the perpendicular distance from the 5s center of the wheel 9 to the moving wire I, I, are so proportioned that the pole pieces of one pick-up coil come into juxtaposition when the preceding coil ceases tobe in juxtaposition to the wire. The connections to the coils II, I2, I3, etc. may be brought to slip rings I5, and contact from the slip rings to the external terminal equipment I6 may be made by way of suitable brushes or mercury contacts. Wire I, I is arranged to travel at v a substantially constant speed. It is essential that wheel 9,- however, be arranged to travel in the same direction as wire I, I, but at a speed greater than twice the speed of wire I, I for reasons `explained later, so that the text of each section or unit of the signals is taken up and repeated in reverse order, that is, inverted by the pick-up coils. Ii speech currents are used, the coils II, I2 and I3, etc., pick up the messages in phonetic inversion and apply them to any suitable amplifying and terminal equipment I6 which serves to transmit the inverted message to the receiving station. In the same manner subsequent signals or portions thereof will be taken off by the following magnet coil on the wheel 9 and thus reproduced.

By making the rotational speed of the pick-up wheel 9 such that the peripheral velocity of the ends of the pole pieces of coils I0, II, I2, etc.

is approximately four times the linear velocity of the magnetized wire I, I, the voice frequencies are tripled and every portion of the speech recorded on the wire is repeated twice, the actual periods of reverse pick-up overlapping each other. This is for two repetitions or sending triple. If only a single repetition is desired, the ratio of scanning velocity to linear velocity of the wires is made three to one. Of course, additional repetitions may be had by driving the wheel at greater speed. The outgoing signal during each scanning period is reversed, with respect to time, from the original.

The receiving equipment for putting the speech or signals back into their original form in sequence is identical with that just described, with the added feature of means for shifting the phase or angular position of the pick-up wheel with respect to the main driving shaft of the synchronized driving motor.

A necessary adjunct to this equipment is a very constant source of low frequency energy for energizing the synchronous motors. Such equipment, having a high degree of frequency stability, is readily available, as known in the art. Suitable frequency control equipment, amplifiers, and combined direct current and synchronous motors built into a single unit may, if desired, be used since these are standard equipment in facsimile systems.

Control of the phase adjustment can be accomplished manually by the circuit attendant, or can be made semi-automatic by transmitting a synchronizing impulse on a modulation frequency above the band used for the voice channel, in a manner well known in the art. In the interest of secrecy such a synchronizing signal should have a periodicity which does not bear a simple relationship to the period of the reversals of speech.

The manner in which repetitions are formed, and later super-imposed upon one another to reproduce the original, is better explained as follows:

Assuming that it is desired to transmit a signal consisting of characters a b `c d e f g h i i and to have a ratio of velocities of wheel to wire of three to one. the scanning length of the wire I, I is divided into three parts. From this it will`be seen that the outgoing signal is in the following order: cba. dcb, edc. fed. We. hai, tha and im. The reproducing equipment at the receiving end lays these signal sections or units down upon the moving wire in the following manner with respect to the receiving pick-up coil 2I and utilization circuit 22:

abc

bcd

cdc

def ef fah ghi

hii

from which it is apparent that every portion of the original has been transmitted in reverse order three times. The result of superposing these sections of the received signals is to reproduce the original message in its correct form and sequence.

For a ratio of velocities of four to one the scanning length should be divided into four parts. The sections of the received signal are superposed as follows:

abcd

bode

cdef

defy

efgh

fahi

chi

This gives quadruple transmission of every portion of the message.

It should be noted that the receiving machine places the incoming signals on the wire I', I by means of the coils I0', II', I2', I3', etc. on the rotating wheel 9', in contradistinction to the original method of recording at the transmitting station by means of a stationary coil 1. This mode of operation is an essential requirement for obtaining multiple repetition operation.

An advantage of the present invention is that it is impossible for chance listeners or for determined eavesdroppers to understand the conversations, unless there is employed the same equipment as used on the circuit, or equipment equivalent to it. Due to the speech being reversed with respect to time rather than inverted with respect to frequency, the fundamental frequencies sent over the circuit are doubled or tripled in comparison with those in the original speech, depending upon the number of repetitions. The system is, therefore, not subject to any greater distortion due to fading than is straight speech.

It will be evident from the foregoing that the present invention may be utilized to record the original voice on photographic film instead of on a wire or disc material, the developed film or reprint being scanned by a suitable light source and optical system equivalent to the pick-up wheel of Figure 1. Three or more light sources and a corresponding number of optical pick-up systems mounted on two endless belts on opposite sides of the iilm and driven at a desired linear velocity greater than that of the film would give the desired reversal of speech in each period.

I claim:

1. The method of transmitting intelligence which comprises making a record of the message to be transmitted, picking up from the record in succession, a plurality of times in the reverse order in which it was recorded, the message or a portion thereof, transmitting the message or a portion thereof so picked up to a distant station and there restoring the message to its original i'orm.

2. The method of transmitting intelligence which comprises recording a signal upon a moving body, subdividing said signal into a predetermined number of signal sections, picking up from said body from immediately succeeding sections the same portions of messages by means of a second body which moves in the same direction as and at'a greater speed than the first mentioned body, transmitting the messages so picked up to a distant point and there restoring them to their original form.

3. The method of transmitting intelligence which comprises making a record of the message to be transmitted, obtaining from said record a plurality of message sections each of which contains a portion oi the message appearing in the immediately preceding message section, and transmitting each message section to a distant station.

4. In apparatus vfor secret signaling, means for consecutively recording signals in their nor-` mal order, means i'or subdividing said signals into a predetermined number of signal sections whereby the same portions oi the message appear in immediately succeeding sections, and means for picking up the signals of each section in inverted order and for transmitting said signais of each section whereby each portion of :ieoi'dcd signal is transmitted a plurality of es.

5. Apparatus foi' secret signaling comprising means for consecutively recording signals in their normal order, means for subdividing said signals linto a predetermined number of signal sections, and means for picking up the signals oi each section in inverted order and for transmitting a portion o! said signals ot each section a plurality of times, a receiving arrangement comprising a movable magnetic band and a rotating device having the same direction ot travel as said band and arranged to record the received signals on said band, said rotating device their original form.

6. In a telephone communication system,

transmitting apparatus comprising a moving band, a microphone, and coil means responsive to current variations in said microphone for establishing on consecutive portions. of said moving band signal recordings corresponding in sequence to the message wave signals, a receiver, a transmission medium between said transmitting apparatus and said receiver, the latter comprising a second moving band and movable coil means coacting therewith for transferring thereto a plurality of times the same signal recordings received from consecutive portions of said ilrst band.

'1. In a telephone communication system, transmitting apparatus comprising a moving band, a microphone, and coil means responsive to current variations in said microphone for establishing on consecutive portions of said moving band recordings corresponding in sequence to the message wave signals, a rotating device forobtaining in inverted order from said bandV a portion of said signals a plurality of times, receiving apparatus comprising a second moving band and a second rotating device cooperating with said last band for transferring thereto each signal portion received from said first band, the speed of said second rotating device being greater than the speed of said second band by an amount sumcient to cause a predetermined overlapping of thesignal portions recorded on said band whereby the signals are restored to their original form.

8. 'I'he method of transmitting intelligence which comprises making a record of the message to be transmitted, obtaining from said record a plurality oi overlapping message sections, each of which contains a portion of the message appearing in both the immediately preceding and succeeding message sections, and transmitting each message section to a distant station.

JOHN' B. MOORE. 

